The present invention relates generally to an antenna array, and more particularly to a high-gain conformal antenna array that can steer its beam direction without the use of phase shifters and beamformer circuitry.
It is often desirable to have antenna arrays that are “steerable,” so that the antenna can be used to communicate while the antenna is attached to a moving object. Typically, these “steerable” antennas are phased array antennas. A phased array antenna usually has a non-mechanically steered array of radiators. The radiating elements are passive devices (e.g., dipoles or feed horns), and may include active devices, such as amplifiers. The steering of the beam is carried out by varying the phase (and amplitude for full side lobe control) of the signal in each radiating element. For a passive device, the phase control typically is achieved in a feed assembly placed between a high-power amplifier and the radiating elements, and for an active array, there typically is a phase shifter and amplifier per element per beam.
For a passive array antenna, the high-power amplifier has had the power divided up among a number of different feed lines. Each feed line is acted on by a variable phase-change and a variable attenuator device. The resultant output signal from each feed line then is fed to a passive antenna element. The sum of the many phases and amplitudes generated by the passive antenna element cluster will develop the antenna beam direction and coverage.
For an active array antenna, the phase and amplitudes are controlled by active elements in each feed line. The amplitude is controlled by the gain of an amplifier, and the phase can either be controlled within the amplifier unit itself or by a phase element associated with the radiating device. To steer the beam, many signal lines will each feed an active element, and a complex phase front will be developed by the array. Each beam direction will be determined by the composite phase of the associated phase front for that signal, and each beam shape will be given by the number of individual elements geometry of the array.
The problem with traditional phased array antennas is that they require large, complex and expensive circuitry to make them work. In the passive array case, the antenna array requires a phase shifter and attenuator for each radiating element. Similarly, in the active array case, the antenna array requires an amplifier and phase shifter for each radiating element. As one skilled in the art will appreciate, these phase shifter or beam-forming networks require a significant amount of power, take-up a significant amount of space, and are quite expensive.
Thus, a need arises for a steerable antenna array system that is relatively easy to implement, requires less power-intensive circuitry, and is less expensive than the traditional phased array antennas.